I have a cf moto 520s/500s and when i changed the sparkplugg i noticed it being white, thtas use to indicate the machine running lean. I'm thinking on whats may have caused it to run lean. I have an uni filter on the machine, i have made a snorkel for the intake recently. I also have removed the catalytic converrter and made the end pipe (the pieceof pipe after the muffler) a bit bigger.

But i do have an 02 sensor in the exhaust and an air ensor in the intake thats are soposed to always keep the machine in the factory fuel mix and not running leaner than factory tuning. So im wondering of some senor or conector to a sonsor starting to akt upp and therefor it's running lean.

for not so long ago i cleaned the intake air sensor. i cleaned the o2 senor when i changed the sparplugg and will check the sparkplugg when i get some km on the new plugg.

I have runed on the sparplugg about 10000km but it shouldn't be white because it has ben used to long right? (the whole plug was white not youst the tip or whts you should cal it)

Do ypu have any suggestion of whats might cause it to run lean ?

when i don't have so much fuel left (still a few litesr) and brake hard then hit the throttle again it starts to starv for uel for a second ot two and backfires and then start accelerating again. Do you think it's because the fuel goes t the front of the tank when i brake or is smething wrong with the fuel system ?

[2015 Z Force 800 53/Trail EPS]

Well, from my experience, these new EFI systems will keep the plugs at or near white at all times. With that said however ..you said you cleaned the O2 sensor..with what? I ask because there is nothing you can use on it that won't leave...something that contaminates it...not even just a brush. I have always been told never attempt to clean one with anything. Just replace it. Your surging issue may be a fuel supply problem and may also be the cause of extra leaning so check the pressure and volume. Also check the tank's check valve.

The EFI system adjusts the fuel trim based on the values returned by the O2 sensor. Cleaning an O2 sensor, while possible, is likely not to be completely effective, and could do more harm than good.

If fuel pressure is OK, then replace the O2 sensor. It couldn't hurt to run a bottle of fuel system cleaner (Techron) through the system before doing so. The plugs on my Z8 were fine last time I pulled them, so the EFI and fuel injectors are doing a proper job.

Removing the CAT isn't going to get you anything and could potentially have a negative impact engine efficiency depending on the EFI map and exhaust tuning.

I cleaned the 02 sensor with a spray can of breakcleaner (did not touch it with anything). did not seem that dirty but i rhought i clean it as i had taken it out to inspekt it.

I have used fuel system cleaner at the begining of this summer. Don't remember what brand but i know it's recomended by car manufactors to use in the fuel to clean the fuel system so it's was a quality produkt.

Whats the tanks "check valve" ?

I removed the cat to get rid of some heat around my legs and it helped a lot. My dad has done that to his 800 and also removed one of the "walls" in the muffler and his 800 still don't make the plug white as mine do. i do run my plugs for a loot longer time then he does and it's not the same machine but i don't think my plugs shold be white.

Do you know any more sensors than the 02 sensor in the exhaoust and one intake air sensor in the intake ? My machie have about 850hours on it and about 24500km on it. o Maybe some things need to be cleaned if I youst know where and how.

Caustic cleaners like brake cleaner can damage the ceramic sensor inside the protective shell of the O2 sensor.
Again, they aren't made to be cleaned. They are pretty sensitive devices.

Mass Air Sensor cleaner is the only cleaner that should be used on the intake T-map sensor.

[2015 Z Force 800 53/Trail EPS]

Caustic cleaners like brake cleaner can damage the ceramic sensor inside the protective shell of the O2 sensor.
Again, they aren't made to be cleaned. They are pretty sensitive devices.

Mass Air Sensor cleaner is the only cleaner that should be used on the intake T-map sensor.

Agreed. You have contaminated the O2 sensor so replace it. Removing the cat converter probably reduced the back pressure which leans it out..may be farther then the system can make up for. I know on my own just taking the spark arrestor out did that.

Are the 02 sensors that sensitive ?

I googled how to clean them and some guys used gasoline and some used carbourettor cleaner and some other cleaners. the breacleaner i used contained:
"Naphtha(petroleum),hydrotreated light"

if i don't find anything else that may caouse the lean running i gues i can test the old end pipe with the spark arrestor in it and se if it makes a difference.

O2 sensors are designed to function in a 600+ degree environment (which is hot enough to burn off most contaminants) and generate precise currents in a very narrow band based on the oxygen content of the exhaust gases. Contaminant buildup on the outer shell is not an indicator of the condition of the inner sensor.

These sensors are not designed for exposure to catalytic or petro chemicals. It should surprise noone that youtube is full of people cleaning the O2 sensor in various ways. You can clean anything. What these folks can't and don't do is test the sensor for in-spec operation before or after the cleaning. You won't find a qualified mechanic recommending cleaning an O2. Etching away the thin film on the sensor will affect the sensor output.

If you are indeed running lean, the O2 and T-Map may be playing a role, along with the exhaust modifications. You can use an ECU monitoring tool to see what the input signals to the ECU are to help determine the cause, and to see if the ECU trim adjustments are against the limits. The dealer should have such a device.